Hearing aids that incorporate a built-in microphone for picking up sounds traveling through the air, an amplifier for amplifying the sounds thus picked up, and a transducer (miniature speaker) for retransmitting the amplified sound, are known. However, if a person with hearing difficulties uses a telephone while wearing a hearing aid of this type, then the internal microphone of the hearing aid amplifies not only the sound transmitted from the speaker of the telephone device, but also the ambient noise, and hence the telephone is not readily usable by a person with hearing difficulties.
In order to eliminate problems of this kind, a magnetic pick-up type hearing aid has been proposed wherein, rather than picking up the sound propagating through the air by means of an internal microphone in the hearing aid, the variations in the magnetic field generated by the voice coil incorporated inside the speaker of the telephone device are picked up by an internal magnetic coil of the hearing aid and are used to drive a transducer. A hearing aid of this kind has a built-in magnetic coil forming a magnetic coupling with the voice coil of the telephone, and as sound is radiated from the speaker, the variations in current induced in the magnetic coil are amplified and used to drive the transducer.
As a reference relating to a magnetic pick-up type hearing aid, Japanese Patent Laid-open No. 2001-094647 is known, for example.
However, when a cordless telephone is used by a person with hearing difficulties, while that person is wearing a magnetic pick-up type hearing aid, then the electromagnetic waves radiated by the cordless telephone handset, and in particular, the electromagnetic waves induced by current variations in the TDD (Time Division Duplex) processing section located in the RF circuit of a digital cordless telephone handset, are also picked up, and hence bothersome noise is output from the hearing aid, thus impeding hearing ability.
It would therefore be a significant advance in the art to provide a cordless telephone handset which does not affect the use of magnetic pick-up type hearing aids.